Several rachidian straightening and stretching devices are already known of, such as those described in French patent applications No. 89 10176 and 91 15455.
Such devices use implants with screws and hooks on which the head features longitudinal grooves at the bottom of which connecting and staying rods, usually milled or fluted on the outside, are locked. The locking of said rods inside the grooves results from the deformation of the groove sides brought together through a cylindrical screw system achieved around the head of the implants and hooks and a tapered bolt which, when tightened, gradually brings together the groove sides and thus causes partial crimping of the rod inside the grooves and the gripping of the rod against the bottom of said grooves through the base of a nut notched to resist any inadvertent unscrewing; various means of longitudinal and lateral connection being provided for.
The purpose of the device under the invention is to permit the straightening, fixation and compression or elongation of the cervical vertebrae, alone or in addition to the rachidian vertebrae, while providing for some lateral offsetting of the bottom clamps in relation to the top clamps in order to take into account some shape differences in the concerned vertebrae, or to maintain a specific alignment with the rods which might already be used on the same patient for rachidian straightening and stretching.
As a matter of fact, regardless of the scoliosis problems which apply to all rachis vertebrae, it happens very often that the cervical vertebrae are accidentally injured, especially upon brutal falls.